Patent GB-1529086-A (GB)
Title: Electronic tdm data switching systems
IPC: H04L12/52
Filed: 1976-01-23
Abstract: 1529086 TDM exchanges SIEMENS AG 23 Jan 1976 [26 Feb 1975] 02585/76 Heading H4K In a method of switching digital data signals from a t.d.m. feeder line to a selected t.d.m. trunk line in a digital data t.d.m. transmission network in which data are transmitted in each line, in bit groups internested in a t.d.m. frame, the bit groups being supplied from respective feeder channels, the position of each bit group in the frame being arranged to correspond to, and so indicate, the feeder channel supplying the bit group, the method includes the steps of supplying the data signals from the feeder line to a switching system supplying a request signal to the switching system indicative of the switching operations to be effected by the switching system, for each received bit group, deriving from its position in the t.d.m. frame a feeder line channel address, enabling a feeder cell in a connection store of the switching system the cell being selected via a switch-through flow control unit on the basis of a pre-assignment of the cell to the relevant feeder line channel address, supplying bit groups during establishment of a connection so as to enter a desired trunk line channel address into the feeder cell, switching through the connection and, following the reception of each bit group, reading out the trunk line channel address from the feeder cell by means of the switch-through flow control unit, supplying each bit group associated with said read out trunk line channel address to the appropriate trunk line, storing the bit groups supplied to each trunk line in respective trunk cells of a switch-through store for forming t.d.m. frames, the trunk cells corresponding to the respective trunk line channel addresses, detecting when a succession of identical bit groups is received from a feeder line channel, inhibiting supply of said request signal to the switching system in respect of bit groups of said succession subsequent to the first bit group of the succession, and repeatedly reading out to the selected trunk line the same bit group from the appropriate trunk cell during said succession. The method is stated to avoid or reduce previous spatial fanning out of T.D.M. channels allowing them to be connected directly to an electronic data switching system. Also envelope (bit group) switching and the use of the switching system only for essential processes subjects the system to minimal load. Each feeder line terminating device may comprise a synchronizing circuit supplying a series parallel converter from which addresses are derived. The embodiment disclosed relates to a known system having a plurality of processing units comprising a line termination unit (LE) (Fig. 1 not shown) normally switching only polarity changes, a programme control unit (PE) and connection unit (GE) (operation of these units is described in detail in "der Fernmeldeingenieur", 26th Edition Vols. 5 & 6). The invention is related to unit (DE) allowing connection of a data transmission line comprising a plurality of T.D.M. channels to the data switching system without, or reducing previous spatial fanning out of channels. Each incoming feeder data line ZDL is matched to the switching system and incoming data is regenerated in DUE, a common timing generator NTG producing three synchronizing pulse trains corresponding respectively to a bit rate, envelope rate (which synchronizes envelopes in SY) and frame rate, the latter establishing position of envelopes within a frame. From SY, envelopes, which may comprise a status bit Z plus 8 data bits, is placed in a serial/parallel converter SPU which interfaces a comparison circuit EB which determines whether the envelope relates to signalling or is an information character and whether it should be switched to an idle channel; SY also feeds address circuit EAZ, comprising a counter, from which, except where the envelope relates to an idle channel, a switching request is directed via channel coder KC and request circuit A to input code converter ECW. Each envelope is compared with a corresponding envelope in the preceding T.D.M. frame and if informational content has changed a switching request is directed through A to ECW; otherwise not. In EB, envelopes of a frame are counted e.g. 1-80 and each related envelope is transferred into store EV; channel coder KC however is permanently set to channels of line ZDL and forms only one feeder line address which is placed in KAZ. Content of EV, KAZ is subsequently transferred, on command from switching request identifier ID, to an input coupler EK and subsequently into further envelope and feeder channel address stores EV, KAZ within input code converter ECW; a multiplexer of known type may be used as input coupler EK. A switching request from a non illustrated coding circuit causes identifier ID to form a feeder line address which is placed into part store LAZ. ID and EK may be connected to line device LEZ assigned to line ZDL and also to all other feeder line devices or alternatively in each case only one group of line devices is connected to its own ECW which will be one of a plurality. With envelope EV, channel address KAZ and line address LAZ in converter ECW, entire bit group is passed into control unit DAS (corresponding in function to a flow control unit as disclosed in German Specification 1946349). If a plurality of converters are provided these are connected to DAS independently of each other. DAS is connected to central storage unit (SE Fig. 1, not shown) also a connection store DVS which embraces a plurality of feeder cells each permanently assigned to one channel. When an entire bit group is offered to DAS, a connection is established via (SE) by control unit (PE) by the address of the required trunk being entered into the appropriate feeder cell. When the connection is established a feeder cell is activated and the trunk address therein is added to the envelope hence DAS effects an interchange of feeder and trunk addresses. Output code converter ACW which may be common for all trunk lines or one of a plurality for respective groups of trunk lines includes an output coupler AK which may comprise a known demultiplexer receiving the envelope EV and trunk address KAA and an output into trunk line devices LEA which is designated by a trunk line address; this is fed into decoder ALD which releases a path to the appropriate device LEA for EV and KAA. Subsequently EV is entered into addressable store DUS accommodating a full frame at an address designated by KAA. Read out of store DUS is particularly simple when each bit group of a frame is assigned a respective channel. A trunk envelope address is formed in EAA in conjunction with a 1-80 counter. If a T.D.M. frame has as many envelopes as channels decoder KD is not necessary in which case envelopes can be read out from DUS by addressing individual storage positions SP by the trunk envelope address. From each selected storage position SP each envelope is entered into a parallel/serial converter PSU where it is transferred to data transmission device DUE to trunk line ADL. If data lines comprise channels of differing speeds, those which belong to a higher speed channel possess the same channel address KAA and these higher speed envelopes are consecutively written into storage position SP of store DUS. To bring the envelope to the correct position in the frame for transmission, channel decoder KD ensures that positions SP 1-20 are consecutively addressed the numbering position 1 corresponding to storage positions 21, 31 etc. which is stated to ensure correct classification of envelopes within frames even with channels exhibiting differing speeds. Channel coder KC and decoder KD may be in the form of gate networks or addressable stores; if the latter, the number supplied by envelope addresses EAZ, EAA is employed as an address thus cells are read out which contain associated channel address KAZ, KAA. Alternatively KC, KD may be constituted together with EAZ, EAA by programmable counters.